The CCITT,considering(a) that to permit the sharing of responsibility for the maintenance of a high-standard of transmission between countries participating in the establishment of switched connections,it is necessary to specify limiting values of distortion at the international terminal exchanges;(b) that on the other hand,to enable national switched networks to be interconnected,it is necessary to have a distribution plan of the telegraph distortion between national networks and the international junction circuits connecting up the international switching centres (international terminal switching centres);(c)that Figure 1/R.58 shows the points of entry and exit of the national network and the ends of the international junction circuit;(d) that it is difficult to lay down standards applicable both to small and to large national networks.However,it has been possible to fix limit values for large countries and they could apply to the great majority of telex subscriber stations or gentex stations taking part in the international service.
ITU-T R.58-1988 Referenced Document
ITU-T R.57 Standard Limits of Transmission Quality for Planning Code-Independent International Point-to-Point Telegraph Communications and Switched Networks Using 50-Baud Start-Stop Equipment - Telegraph Transmission (Study Group IX) 2 pp*， 1989-01-01 Update
ITU-T R.58-1988 history
1988ITU-T R.58-1988 STANDARD LIMITS OF TRANSMISSION QUALITY FOR THE GENTEX AND TELEX NETWORKS